1. Field of the Invention
The present invention relates to a reflective photosensor and a semiconductor light emitting apparatus each employing a micro Fresnel lens.
2. Description of Related Art
FIG. 22 illustratively shows an example of an reflective photosensor in which a light emitting element and a light receiving element are disposed in a housing or an armouring of the photosensor.
The configuration of the reflective photo sensor includes a light emitting element 102 such as a light emitting diode, a light receiving element 103, for example, a light receiving diode, a focusing lens 104 for the light emitting element 102, and a focusing lens 105 for the light receiving element 103. The constituent components are disposed in a mold resin structure 106 as an armouring or a housing of the reflective photosensor.
Furthermore, the light emitting element 102, the light receiving element 103, and the lenses 104 and 105 are respectively arranged in an inclined state in the mold resin 106. In consequence, a light emitted from the light emitting element 102 is irradiated from an inclined direction onto an object to be sensed 107. In addition, a light reflected from the object to be sensed 107 with a predetermined angle enters the light receiving element 103.
However, in the structure of the conventional reflective photosensor, the light forcusing lenses 104 and 105 are respectively disposed for the light emitting element 102 and the light receiveing element 103, which hence increases the number of constituent components and the number of assembly steps. Furthermore, the setting of an angle between the light emitting element 102 and the light receiving element 103 as well as an optical axis adjustment of the focus lenses 104 and 105 with respect to the arrangement of the above elements 102 and 103 are required to be carried out in consideration of a distance between the sensor and the object to be sensed 107. As a results, the assembly process becomes complicated.
On the other hand, in an apparatus using a light such as an optical information recording and playback apparatus, a semiconductor light emitting apparatus is employed as a light source of a collimated light or a focused light. FIG. 23 shows an example of a semiconductor light emitting apparatus of this type. In this configuration, a laser diode 111 emits a laser light, which is collimated or focused by a group of aspherical lenses 112 to be radiated as a collimated or focused light. The apparatus of FIG. 23 comprises a monitor photodiode 113 disposed to stabilize the power of the laser light emitted from the laser diode 111.
The conventional semiconductor light emitting apparatus however is attended with the following problems.
Since a group of aspherical lenses are used, the overall size of the system is increased, which results in an heavy weight of the configuration.
Owing to the usage of a laser diode as the light source, a countermeasure for stabilization of the power of light is necessary. Namely, in addition to the monitor diode, there is necessitated an output stabilization circuit including a pre-amplifier, a reference power source for determining a threshold level, a differential amplifier, a power amplifier, etc.
The laser diode has in general a relatively short life; moreover, the reliability thereof is not satisfactory for the system.
In a case where a laser light reflected from a recording medium is adopted as a playback signal light and/or a control light for a tracking servo and a focusing servo, the safety standards are necessarily to be observed. Namely, the user is required to pay great attention to the safety standards in the operation.